This invention relates to magnetically responsive imaging compositions; and, more particularly, to compositions comprising a ferrofluid.
There has recently been introduced an magnetic imaging system which employs a latent magnetic image on a magnetizable recording medium which can then be utilized for purposes such as electronic transmission or in a duplicating process by repetitive toning or transfer of the developed image. Such latent magnetic image is provided by any suitable magnetization procedure whereby a magnetized layer of marking material is magnetized and such magnetism transferred imagewise to the magnetic substrate. Such a process is more fully described in U.S. Pat. No. 3,804,511 to Rate et al.
The latent magnetic image, by way of analogy to xerographic imaging, is developed with a magnetic developer to render the latent magnetic image visible. The developed, visible, magnetic image is then typically transferred to a receiver such as, for example, a sheet of paper to produce a final copy or print. This final copy or print is typically referred to as hard copy.
Concurrently with the growth of interest in magnetic imaging, there has been a growth of interest in magnetic developers to render the latent magnetic images visible.
For example, U.S. Pat. No. 3,221,315 to Brown et al. is directed to the utilization of encapsulated ferrofluids in a magnetic recording medium wherein the ferrofluid orientation in the presence of a magnetic field exhibits a variable light-responsive characteristic. In this case, the magnetic recording medium is self-developing in the sense that magnetic marking material need not be employed to present a visible image. In other situations, latent magnetic images are rendered visible by magnetic marking material. For example, U.S. Pat. No. 3,627,682 to Hall et al. is directed to binary toners for developing latent magnetic images. These binary toners include a particulate hard magnetic material and a particulate soft magnetic material in each toner particle. The toner particle includes these two materials and a binder material. For dry development, the toner particles are mechanically mixed with polystyrene beads to form a two component developer.
In addition to magnetic marking material being applied directly to the latent magnetic image, there is also interest in novel compositons and techniques useful for rendering latent magnetic images visible. For example, U.S. Pat. No. 3,013,206 to Youngquist et al. discloses a magnetic reader comprising a hollow non-ferromagnetic vessel having a cavity field with a suspension of flat, visible, weakly ferromagnetic crystals which orient when suspended in the liquid and in response to a magnetic field.